Yes. The Vermont Department of Health recommends testing homes for radon and specifically advises testing before and after renovations, especially repairs that reduce radon levels or changes that increase time spent in a basement. Waterproofing, encapsulation and air sealing can change pressure and airflow, so a post-work test confirms the actual result. Encapsulation is not itself a radon test or a guaranteed mitigation system.
What to know
- Test rather than guessing; radon has no smell or visible sign.
- Consider a baseline test before major lower-level work.
- Retest after encapsulation, air sealing or waterproofing changes.
- Use a certified radon mitigator when the result calls for action.
Why lower-level work can matter
Radon enters from soil through cracks, joints and openings and is affected by the construction and operation of the home. A liner, sealed crawlspace, new drain, sump cover or major air-sealing project can change the openings and pressure relationships in the lower level.
Those changes may help a future mitigation system, but the finished radon level cannot be predicted from the moisture work alone. Testing is the only way to know what happened.
What Vermont recommends
The Vermont Department of Health recommends long-term testing for three to twelve months when time allows, ideally including a heating season. Medium- and short-term tests are also available when a faster result is needed.
Vermont lists 4.0 pCi/L as the action level and encourages reducing levels below 2.0 pCi/L when practical. The Department recommends a certified mitigation contractor when action is needed.
Before and after the project
If the project is not urgent, a baseline test provides useful information before the space changes. Tell the waterproofing or encapsulation company about an existing mitigation system so drains, sump covers, liners and vent piping can be coordinated.
After the project, follow the test kit instructions and use a certified laboratory or qualified tester when required for a transaction. Keep the result with the project records and test an operating mitigation system at the interval Vermont recommends.
- Document the pre-work result
- Keep mitigation components accessible
- Seal liner and sump details as designed
- Retest after the work
- Retest an operating mitigation system every two years
What waterproofing does not prove
A dry basement can still have elevated radon, and a damp basement does not establish the radon level. A vapor barrier can be part of a mitigation design, but ordinary encapsulation does not guarantee a particular reading.
Keep the scopes clear: waterproofing controls water, encapsulation controls ground vapor and air exchange, and a radon system is designed and verified to reduce radon.
What to measure and when
Waterproofing and encapsulation change how air and moisture move in the lower level, and radon is a gas that follows air. That is why it is measured separately, before and after the work, and not assumed to have stayed the same.
| Stage | What to do | Why |
|---|---|---|
| Before the project | Test for radon | Gives a baseline to compare |
| During | Ask how new penetrations and seams are sealed | Openings are a path for soil gas |
| After | Test again under normal conditions | Confirms the change, if any |
| If the result is elevated | Have mitigation designed | Waterproofing does not lower radon |
Sources and Vermont specifics
What the state says about retesting
The Vermont Department of Health reports that one in seven Vermont homes has elevated radon, and that the action level is 4.0 pCi/L: at or above it, the Health Department and EPA recommend reducing radon levels. It advises retesting every five years or whenever significant changes are made to a home's structure or mechanical systems, and says short-term testing may be done in a basement that will be used as living space.
Waterproofing and encapsulation qualify as significant changes. A test taken before the work gives you a baseline, and a second test after the system has run through a normal season shows whether the work changed the result. Keep both and give them to whoever buys the house.
Buy or borrow a test kit before the work starts, follow the instructions closely and place it in the lowest lived-in level. Closed-house conditions for the test period matter, so avoid opening windows and running large fans. If the first result is below the action level, you have a baseline. If it is at or above 4.0 pCi/L, ask the contractor whether a mitigation pipe can be integrated into the sump or drain layout before the slab is patched.
Sources: Vermont Department of Health, Radon. Checked September 26, 2026.
Frequently asked questions
What radon level should prompt action?
Vermont lists 4.0 pCi/L as the action level, and the Health Department and EPA encourage taking action to lower levels below 2.0 pCi/L. Vermont notes the average indoor level in homes is about 2.5 pCi/L. Testing is the only way to know, because radon has no colour, smell or taste.
Does a sealed sump cover reduce radon?
A gas-tight cover can be an important part of a radon system, but the cover alone does not prove the home's radon level is acceptable. Test after the work.
How long should a Vermont radon test run?
Vermont says a three- to twelve-month long-term test gives the best picture when time allows. Short-term tests can be used when a faster result is needed, including some real-estate situations.
Sources
General information, not a diagnosis of your property. Editorial policy